SQL, using entered time to find session with most visitors

问题

I have a query that I need to write. Lab assistants will enter the information for students coming to the lab for help. the field are:

Visit_ID, Student_ID, Visit_Date, Time_In, Time_Out, Course, Asst_ID.

There are 3 sessions for time_in entry

• Session 1 9-12
• Session 2 12-3
• Session 3 3-6

The query needs to determine which session on the current day had the most visitors. This is what I have so far:

with cte as
 (
  select 
      case
        when cast(Time_In as time) >'12:00:00' and cast(Time_In as time) <='15:00:00'  and Visit_Date = cast(GETDATE() as date)then 'Session 2' 
        when cast(Time_In as time) >'3:00:00' and cast(Time_In as time)<= '6:00:00' and Visit_Date = cast(GETDATE() as date) then 'Session 3'
        else 'Session 1'
      end session
      /*course*/
    from Lab_Visits2
  ), ctecnt as (
  select session,/* course,*/ count(*) cnt
  from cte
  group by session /*course*/
)
select session, /*course,*/ (cnt)
from (
  select session, /*course,*/ cnt, row_number() over (order by cnt desc) rn
  from ctecnt
  ) t
where rn = 1

来源：https://stackoverflow.com/questions/28843265/sql-using-entered-time-to-find-session-with-most-visitors